Purification of metal hydroxide solutions by means of electrolysis wherein the metallic ions are removed from the solution and deposited on a porous carbon electrode is described in U.S. Pat. No. 3,459,646. In that prior art system, the cathode is a porous block of carbon or graphite supported across a liquid flow path and through which the electrolytic solution to be treated is passed. An anode electrode is mounted in proximity to either the upstream or downstream side of the cathode to develop a steady DC electric field between the anode and cathode whereby to cause the metallic ions in the solution passing through the pores in the cathode to separate out of solution and be plated onto the interior surfaces of the carbon electrode. After the pores have become substantially plugged by the deposited ions it is necessary to interupt the operation and remove the metallic ions from the pores of the carbon electrodes by, for example, reversing the polarity of the system, chemically treating the carbon electrode with an acid solution or replacing the carbon electrode. The down time of the system is, therefore, substantial whereby two such systems would be required for each overall purifying system with which this process is to be employed.
Moreover, when this prior art electrolytic metal removal system is to be used in the metal plating industry to purify plating solutions prior to emission thereof to the local sewer system or nearby stream, it is still necessry to remove other objectionable materials from the plating effluent by other means. Such objectionable materials commonly found in such solutions are phosphates and organic molecules and compounds. Additional equipment is thus necessary for this additional purification.